I'm still not quite sure, where you see the contradiction.
Have a look at how Jesus taught the law: saying it’s not what goes into the mouth that makes people unclean, but what comes out of it; saying the Sabbath was made for men and not the other way around, summarizing the law under the two great commandments …
Surely if we truly believe in Him it follows that we’ll at least try to act according to His spirit when it comes to interpret the law in light of these two comandments. Otherwise our belief would just be an empty lip-service. But of course being merely human, we’ll still get things wrong. Hence the cross, which manifests God’s grace.